Fine pattern forming method

Abstract

Disclosed is a fine pattern forming method which is capable of forming a high positive-to-negative reversal pattern high in dry-etch resistance, at high density, by irradiating an entire surface of a resist with ion shower at low doses before or after electron beam or focus ion beam exposure, and then developing it.

We claim: 
     
       1. A method for forming a fine pattern of a double-layered photoresist comprising the steps of: a. coating a semiconductor substrate with a high molecular weight organic resist as a lower resist of said double-layered photoresist;   b. coating said high molecular weight organic resist with a positive resist as a upper resist of said double-layered photoresist, wherein said positive resist is insoluble in a developer;   c. irradiating an entire surface of said positive resist with at least one of H and Si ions in batch at a dosage, whereby said positive resist becomes soluble in said developer;   d. exposing a portion of said positive resist selectively to electron beams or focused ion beams at a dosage, whereby the selectively exposed portion of said positive resist again becomes insoluble in said developer and has high dry etch resistance;   e. developing said positive resist to form a positive-to-negative reversal pattern of said positive resist; and   f. etching said high molecular weight organic resist by using said positive resist pattern as a mask.   
     
     
       2. The fine pattern forming method according to claim 1, wherein the positive resist is PMMA and the ion irradiation of step c. is carried out at an accelerating voltage of 10 to 40 kv, and at a dosage of 5×10 13  to 9×10 13  ions/cm. 
     
     
       3. A method for forming a fine pattern of a double-layered photoresist comprising the steps of: a. coating a semiconductor substrate with a high molecular weight organic resist as a lower resist of said double-layered photoresist;   b. coating said high molecular weight organic resist with a positive resist as a upper resist of said double-layered photoresist, wherein said positive resist is insoluble in a developer;   c. exposing a portion of said positive resist selectively to electron beams or focused ion beams at a dosage, whereby the selectively exposed portion of said positive resist becomes soluble in said developer;   d. irradiating an entire surface of said positive resist with at least one of H and Si ions in batch at a dosage, whereby the exposed portion at step c. of said positive resist again becomes insoluble in said developer and has high dry etch resistance, and unexposed portion at step c. of said positive resist becomes soluble in said developer;   e. developing said positive resist to form a positive-to-negative reversal pattern of said positive resist; and   f. etching said high molecular weight organic resist by using said positive resist pattern as a mask.   
     
     
       4. The fine pattern forming method according to claim 3, wherein the positive resist is PMMA and the ion irradiation of step d. is carried out at an accelerating voltage of 10 to 40 kv, and at a dosage of 5×10 13  to 9×10 13  ions/cm.